Method of measuring a chemical vapor concentration

ABSTRACT

A method of measuring a chemical vapor concentration is provided. A chemical vapor sensor measures a chemical species of interest with high sensitivity and chemical specificity. In an aspect, an ethanol vapor sensor is provided, sized for being inconspicuous and on-board a vehicle, having a passive measurement mode and an active breathalyzer mode, for detecting a motor vehicle driver that exceeds a legal limit of blood alcohol concentration (BAC), for use with vehicle safety systems. For the passive mode, a vapor concentrator is utilized to amplify a sampled vapor concentration to a detectable level for use with an infrared (IR) detector. In an aspect, ethanol vapor in a vehicle cabin is passively measured and if a predetermined ethanol level is measured, a countermeasure is invoked to improve safety. In an aspect, an active breathalyzer is used as a countermeasure. The active breathalyzer can be imposed for a number of vehicle trips or for a predetermined time period.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application and claims the benefitunder 35 U.S.C. §121 of U.S. patent application Ser. No. 11/903,141filed Sep. 20, 2007 which is a divisional application and claims thebenefit under 35 U.S.C. §121 of U.S. patent application Ser. No.11/033,703, now U.S. Pat. No. 7,279,132, filed Jan. 12, 2005.

TECHNICAL FIELD OF INVENTION

The invention relates generally to a chemical vapor sensor, and moreparticularly to actively and passively measuring, with high sensitivityand chemical specificity, a chemical species of interest, for use withsafety systems.

BACKGROUND OF THE INVENTION

Intoxicated drivers are a major cause of traffic accident fatalities inthe United States. A NHTSA report showed that 40% of the total accidentfatalities in the U.S. in the year 2003 were alcohol related. Morespecifically, 12,373 motor vehicle occupants were killed in crashes thatinvolved a blood alcohol concentration (BAC) of 0.08% or higher. Thisequates to over 33% of the 37,132 U.S. motor vehicle fatalities in 2003.In addition to the societal impact, the cost of such crashes in the U.S.is about $40 billion per year. It is well established that the rate offatal traffic accidents per mile traveled is related to a driver's (BAC)and that there is a correlation between impairment in driving skills andthe driver's BAC. The definition of drunk driving in the U.S. involves aBAC level of either 0.08% or 0.10%, depending on the particular statelaw. A primary countermeasure to combat drunk driving in the U.S. is thecriminal justice system, which employs deterrents and sanctions againstdrunk drivers. Various other approaches to combat drunk driving havebeen utilized. The following existing approaches require activeinvolvement of a vehicle driver.

Ethanol concentration in human breath is a good indication of BAC.Inside the air sacs in the human lung, there is a chemical equilibriumbetween the concentration of ethanol in the air and the concentration ofethanol in an individual's blood. An approach to combat drunk driving,which utilizes this notion of ethanol concentration in human breath,uses an electrochemical sensor to measure ethanol concentration in air.For law enforcement purposes, an electrochemical sensor is built into anobject such as a clipboard or flashlight that a police officer can,under certain circumstances, justifiably insert into a vehicle. However,currently available electrochemical sensors have a limited lifetime andtypically must be replaced after about three years. To be used as anon-board component of the safety system, an ethanol sensor must have alifetime of at least ten to fifteen years.

An additional approach to combat drunk driving uses a heated film ofmetal oxide that changes electrical resistance in response to ethanolconcentration. Such sensors are used in commercially available “breathinterlocks,” sometimes mandated following a drunk driving conviction,which require the driver to breathe into a tube to check for excessbreath alcohol before the vehicle will start. However, such sensors donot have sufficient sensitivity for passive detection of a drunk driverin regard to measuring ethanol vapor in the air of a vehicle cabin. Thebreath sample blown into a tube is undiluted so the detection levelneeded is only about 210 parts per million (ppm) ethanol by volume.Also, the minimum ethanol concentration that can be reliably detectedwith a metal oxide film is typically in the range of 10 to 50 ppm. Afurther disadvantage is that the response to ethanol concentration isnon-linear as a function of ethanol concentration.

A further approach to combat drunk driving uses an electrochemicalsensor that is pressed against an individual's skin to determine alcoholintoxication through remote detection of ethanol that evaporates fromthe driver's skin. This approach is an active system since contact withthe driver's skin is required. The lifetime of this sensor has not beendemonstrated.

U.S. patents have been issued for approaches that combat drunk drivingthat involve passing infrared through one of the driver's extremities,such as a finger, or using Raman spectroscopy to measure theconcentration of ethanol in the fluid at the surface of the driver'seyes (i.e., U.S. Pat. No. 6,574,501). These approaches are impracticalfor on-board vehicle use as well.

Further approaches to combat drunk driving exist. The followingapproaches are passive since active involvement of the driver is notrequired. For example, monitoring a vehicle driver's eyes to determinedriver intoxication has been attempted. The direction of the driver'sgaze is monitored as they visually follow a moving object. It isbelieved that an intoxicated person moves their gaze direction in jumpsrather than following an object's motion smoothly and continuously.

U.S. Pat. No. 7,095,501, assigned to Delphi Technologies, Inc., providesincreased sensitivity with a short path length by using a vaporconcentrator. Ethanol vapor is collected by passing air that containsethanol vapor over an adsorber for a period of time. The adsorber isthen heated to release the ethanol vapor. Sensors are utilized thatdetect ethanol vapor by measuring its effect on the electricalconductance of a heated metal oxide film on a ceramic substrate.

Infrared detection has been used to quantify ethanol concentration inbreath for law enforcement purposes, but the instruments used typicallyhave a path length of about 1 meter making them large and bulky. Forpassive sensing in a vehicle cabin, utilizing this instrument, infrareddetection would require a path length on the order of 100 meters. Thisis impractical for an on-board sensor. Moreover, in the case ofrequiring a BAC test before vehicle usage, the passive sensing systemsrequire an extended collection time for collection of vehicle cabin airthat is also diluted air.

BRIEF SUMMARY OF THE INVENTION

A chemical vapor sensor is provided that can actively and passivelymeasure a chemical species of interest with high sensitivity andchemical specificity in a selected area, for use in safety systems. Inan embodiment, the present invention provides for optical detection ofethanol for use in motor vehicle safety systems. A practical sizedon-board sensor is provided having a passive measurement mode and anactive breathalyzer measurement mode.

In an embodiment, ethanol vapor in a vehicle cabin is passively measuredand if a predetermined ethanol level is measured, a countermeasure isinvoked that involves vehicle occupant action to improve safety. In anembodiment, the active breathalyzer is used as a countermeasure(substitutive or duplicative) to the passive measurement mode. Thedriver is required to supply a breath sample to the active sensor priorto one or more subsequent vehicle trips, preventing vehicle startup ifbreath is not supplied or if the measurement test is failed.Alternatively, the breath sample requirement can be imposed for apredetermined time period. In another embodiment, passengers are warnedor required to fasten and utilize seat belts if a predetermined ethanollevel is measured by the passive measurement mode. Additionally, acombination of the above mentioned countermeasures can be imposed.

Regarding the passive measurement mode, ethanol vapor (and optionallycarbon dioxide) in a vehicle cabin is measured, and sufficientsensitivity is provided to passively detect a motor vehicle driver (notrequiring active involvement by the driver) that exceeds the legal limitof blood alcohol concentration (BAC). At the threshold of intoxication,the concentration of ethanol in breath is legally defined as 0.08 gramsof ethanol per 210 liters of breath, which at 1 atmosphere pressure isequivalent to 210 ppm ethanol by volume. The concentration of ethanol inbreath is proportional to the BAC of a person. In an embodiment, thepresent invention provides for passive detection of driver intoxicationby employing a passive chemical vapor sensor to measure both ethanolconcentration in the range of 0.1 ppm to 10 ppm by volume and carbondioxide concentration in the vehicle cabin, and using the measurementsof ethanol and carbon dioxide to infer the BAC of the driver.Additionally, since drivers can exhibit a BAC of much greater than 0.08,and the vehicle cabin air may be less diluted, the present inventionfurther provides for measuring ethanol concentrations greater than 10ppm. Alternatively, the present invention passively detects driverintoxication by measuring ethanol vapor in the vehicle cabin andcomparing the measured level with a predetermined threshold level. In anembodiment, in comparison to known systems, the present inventionincreases the sensitivity of detection of ethanol vapor by a factor ofabout 1,000. Further, the sensor can be situated in an inconspicuouslocation and operate independently without requiring active involvementby a driver.

Regarding the active breathalyzer measurement mode, ethanol is measureddirectly from a driver's breath to detect whether the driver exceeds thelegal limit of BAC. The breath sample blown is undiluted and, asdiscussed above, the necessary detection level is about 210 ppm ofethanol. Further, the active breathalyzer measurement mode can resolveambiguity as to whether an exceeded BAC of ethanol measured by thepassive measurement is due to intoxicated passenger(s), rather than anintoxicated driver.

If a predetermined concentration of a chemical species is exceeded, asmeasured by the passive chemical sensor, the safety system requires thata vehicle occupant perform an action that increases safety. As anexample, the safety system can include setting an ethanol flag to afailure setting and preventing the vehicle engine from restarting untilthe ethanol flag setting is reset to a pass setting as measured by theactive breathalyzer. The safety system can require an activebreathalyzer test for a predetermined number of vehicle trips and/or itcan require the active breathalyzer test for a predetermined timeperiod. In particular, to minimize time inconvenience to a driver in thecase of a safety system preventing vehicle starting, the passivemeasurement mode can be bypassed, and the ethanol detector used for thepassive measurement mode can be used for a quick breathalyzermeasurement. The safety response can further impose requirementsincluding requiring minimum headway distance behind a preceding vehicle,as well as constrain vehicle performance. Additionally, the safetyresponse can include warning passengers to fasten seat belts.

In regard to the passive measurement mode, features of the invention areachieved in part by increasing the sensitivity of detection of achemical vapor. A vapor concentrator is utilized to amplify chemicalvapor concentration to a detectable level for use with an infrared (IR)detector. In the case of detecting ethanol, air is passed through anadsorber for a predetermined time to collect ethanol vapor. The air flowis stopped and the adsorber is heated to release a higher concentrationof ethanol vapor into an infrared (IR) absorption cell. The ethanolconcentration is amplified by about two orders of magnitude due toheating the adsorber. Infrared transmission by an IR source to an IRdetector is used to detect the ethanol. An IR filter limits IR detectorresponse to a band that is absorbed by ethanol vapor. Additionally, amicrocontroller instructs and carries out an appropriate safety systemresponse if a predetermined concentration of a chemical species isexceeded.

A single channel of infrared detection is utilized, and consequently thepresent invention is less costly to implement. Further, since areference channel is made unnecessary, spurious infrared absorption atthe infrared wavelength of the reference channel is not a concern.Additionally, when measuring a chemical species, time resolution is notlimited by the thermal time constant of the IR source, resulting in asimplified system having improved performance.

In regard to the active breathalyzer measurement mode, features of theinvention are achieved in part by passing a breath sample directly intoan IR absorption cell (rather than through an absorber as in the case ofthe passive measurement mode). Like the passive measurement mode,however, infrared transmission by an IR source to an IR detector is usedto detect the ethanol. An IR filter limits IR detector response to aband that is absorbed by ethanol vapor. Again, the microcontrollerinstructs and carries out an appropriate safety system response if apredetermined concentration of a chemical species is exceeded.

Other features and advantages of this invention will be apparent to aperson of skill in the art who studies the invention disclosure.Therefore, the scope of the invention will be better understood byreference to an example of an embodiment, given with respect to thefollowing figures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated by reference to thefollowing detailed description, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a diagrammatic sectional view of components of a chemicalsensor including an active sampling tube, passive sampling tube, vaporconcentrator and microcontroller, in accordance with an embodiment ofthe present invention;

FIG. 2 is a logic diagram illustration of the active and passivemeasurement of ethanol vapor by the chemical sensor of FIG. 1, inaccordance with an embodiment of the present invention;

FIG. 3 is a method step illustration of the passive measurement ofethanol vapor with high sensitivity and chemical specificity, inaccordance with an embodiment of the present invention;

FIG. 4 is a graphical illustration of an example measured voltage as afunction of time from the IR detector as in FIG. 1, in accordance withan embodiment of the present invention;

FIG. 5 is a graphical illustration of an example measured IR sensorsignal ratio versus ethanol concentration, in accordance with anembodiment of the present invention;

FIG. 6 is a graphical illustration of an example measured voltage as afunction of time from the IR detector as in FIG. 1, where concentratedsample vapor is held in an infrared absorption cell for a predeterminedand desired time, in accordance with an embodiment of the presentinvention;

FIGS. 7A, 7B and 7C is a diagrammatic view showing alternativeplacement/mounting options of the passive sensing intake in a vehiclecabin for the chemical sensor as in FIG. 1, in accordance with anembodiment of the present invention; and

FIGS. 8A and 8B is a diagrammatic view showing alternative placementoptions of an active sensing intake for the chemical sensor as in FIG.1, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments are described with reference to specificconfigurations. Those of ordinary skill in the art will appreciate thatvarious changes and modifications can be made while remaining within thescope of the appended claims. Additionally, well-known elements,devices, components, methods, process steps and the like may not be setforth in detail in order to avoid obscuring the invention. Further,unless indicated to the contrary, the numerical values set forth in thefollowing specification and claims are approximations that may varydepending upon the desired characteristics sought to be obtained by thepresent invention.

Presently, in the United States, a driver is legally deemed intoxicatedwhen exhibiting a blood alcohol concentration (BAC) of 0.08%, andtherefore violating the law if operating a motor vehicle whileintoxicated. Passively monitoring a motor vehicle driver's BAC canfacilitate avoiding motor vehicle accidents caused by intoxicateddrivers. The BAC measurement can be utilized to instruct a vehicle toshut down or compensate for the effect of BAC on the driver's reactiontime. Passive monitoring (rather than active) senses the vehicledriver's BAC without active involvement of the vehicle driver. However,conventional ethanol vapor sensors are unsuitable for on-board passivedetection of drunk drivers in regard to monitoring ethanol concentrationin the air of a vehicle cabin. Additionally, actively monitoring a motorvehicle driver's BAC can facilitate preventing intoxicated persons fromeven operating motor vehicles.

A vapor sensor based on infrared transmission requires an appropriatepath length. If the path length is too short, the change in detectedintensity is small relative to the fluctuations in detected intensity.If the path length is too long, the detected intensity at the center ofan absorption line is small. The optimum path length depends upon thechemical concentration that is to be measured. Consider, for example, asensor that measures the fraction of light transmitted in a fixed bandof optical frequency. For improved accuracy the species of interestshould maintain on the order of 10% absorption in the band. Inconventional chemical sensors, an absorption band near 1070 cm⁻¹ (9.4 μmwavelength) is typically used to detect ethanol vapor. Near the peak ofthe 1070 cm⁻¹ band, the absorption coefficient is about 2.5×10⁻⁴(μmol/mol)⁻¹ m⁻¹. Consequently, with an ethanol concentration of 250ppm, a path length of 0.7 m is needed to obtain 10% absorption. At thethreshold of intoxication, the concentration of ethanol in breath isabout 210 ppm (by volume) with 1 atmosphere total pressure. Forcomparison, to determine the concentration of ethanol vapor in a breathsample, law enforcement typically uses an infrared-based instrument thathas a 1 m path length through the breath sample.

However, for passive monitoring of ethanol, vehicle cabin air ismonitored (rather than direct monitoring of a driver's breath) and anethanol sensor consequently requires the ability to monitor asignificantly reduced ethanol concentration. As further detailed below,to detect a driver with a BAC near the threshold of legal intoxication,an ethanol sensor employing passive monitoring must be capable ofmeasuring ethanol in the range of 0.1 ppm to 10 ppm in the cabin of avehicle. Additionally, since drivers can exhibit a BAC of much greaterthan 0.08, and the vehicle cabin air may be less diluted, a passiveethanol sensor must be capable of measuring ethanol concentrationsgreater than 10 ppm. If an infrared sensor is to be used to measure anethanol concentration on the order of 1 ppm, the optimum path length fora commercially available sensor would be on the order of 100 meters (m).It is plainly recognized that the necessity of a 100 m path lengthlimits its use in a vehicle. Thus, commercially available ethanol vaporsensors are too bulky for on-board use, requiring a long path length forinfrared sensing.

The present invention provides, in part, a vapor concentrator (asfurther described below) that increases ethanol concentration to a levelneeded by an infrared (IR) detector for passive detection with vehiclecabin air, and therefore enables the detection of sub-ppm concentrationsof ethanol. Further, the present invention improves chemicalselectivity.

The following experimental examples are provided for illustrativepurposes and are not intended to be limiting.

The ethanol sensitivity needed to passively detect a driver at thethreshold of intoxication is additionally determined by the presentinvention. Carbon dioxide that is naturally present in human breath isused as a tracer to determine sensor measurement requirements(sensitivity required) for passive detection of ethanol in a vehiclecabin. This avoids the use of intoxicated human subjects. Ethanol andcarbon dioxide do not separate significantly as exhaled breath driftsfrom a driver's mouth to a location where air is sampled by the passivesensor. The transport of both ethanol vapor and carbon dioxide from adriver's mouth to the sensor is dominated by convection, which is thesame for both ethanol and carbon dioxide. The concentration of ethanolvapor in breath is proportional to BAC, and is 210 ppm when BAC is0.08%. The concentration of carbon dioxide in exhaled breath isapproximately 36000 ppm (as compared to 370 ppm in ambient air). Likeethanol, carbon dioxide in exhaled breath comes from exchange with bloodin the alveolar sacs in the lung. Based on carbon dioxide measurementswith a test subject, the breath alcohol concentration at the sensor isat least 0.5 ppm for any HVAC setting (with the windows closed) at 5minutes after a driver with BAC of 0.08 is seated in the vehicle, andcan be as high as 10 ppm and even higher for some vehicles. A number ofdrivers breathe only half as much air as the test subject, so theethanol sensor requires sensitivity to 0.2 ppm ethanol in air. Somepeople have driven with a BAC substantially above the threshold ofintoxication, as much as 0.40 and even greater. Further, people thathave recently undergone physical exertion can breathe at a volumetricrate by an order of magnitude higher as compared to a test subjectperson. Therefore, the passive sensor must be capable of measuringethanol concentration by a factor of 50 or higher than theabove-mentioned concentration of 10 ppm.

A system and method is described herein for providing a practical sizedon-board sensor having both a passive measurement mode and an activebreathalyzer measurement mode.

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 illustratescomponents of the chemical sensor 100, which includes active sensingintake 108, passive sensing intake 110, a vapor concentrator comprisingadsorber 114 and heater 116, and microcontroller 140.

In the case of passive sensing, air is drawn into passive sensing intake110 by means of air pump 130, passes through check valve 128, adsorber114 and IR absorption cell 120, and released through air out 134. Airpump 130 is, for example, model TD-3LS from Brailsford and Company, Inc.Check valve 128 is positioned in series to obstruct air flow when airpump 130 is off. Check valve 128 is further useful to prevent flowleakage when active sensing intake 108 is alternatively employed.Adsorber 114 adsorbs ethanol vapor and is heated by heater 116. Adsorber114 can be comprised of carbon such as carbon molecular sieves,activated carbon, and carbon nanotubes. Alternatively, adsorber 114 canbe comprised of a porous organic polymer or an inorganic material havinga high surface area such as a zeolite. Adsorber 114 is, for example, a 3mm long bed of Carboxen 1003 in a glass tube from Supelco. Heater 116can be constructed by winding resistive wire around a glass tube thatencloses adsorber 114, and fastening the resistive wire to the glasstube utilizing epoxy. IR source 118 passes infrared waves across IRabsorption cell 120 to IR filter 124, for measurement by IR detector126. IR source 118 is, for example, an electrical heater, which can beactivated by controlling the current. A broad-band emitter such as anIon Optics source, part number NL5NCC can be employed for IR source 118,when employing a 9.4 micron wavelength band. NL5NCC consists of heatedfilament (in air) with a calcium fluoride window that separates it froman IR cell. The calcium fluoride window is transparent at thiswavelength. Similar devices that emit IR by using electrical power toraise a wire or film to an elevated temperature are available from othermanufacturers. When employing a 3.4 micron wavelength band, IR source118 can also be, for example, an incandescent lamp. IR filter 124 isused to select a range of infrared frequency or wavelength that isadsorbed by ethanol. IR detector 126 can be a thermopile employed todetect IR. The thermopile converts the incident IR into heat and uses aseries array of thermocouples to measure the induced temperature rise.IR detector 126 provides an output voltage as a function of time. Amicrocontroller 140 instructs and coordinates (through signal lines 142)the predetermined operation of chemical sensor 100 components includingair pump 130, heater 116, IR source 118 and IR detector 126.

In the case of active sensing, an undiluted sample (such as sample humanbreath) is forced into active sensing intake 108. The undiluted samplepasses through check valve 122, IR absorption cell 120, and is releasedthrough air out 134. Check valve 122 is useful to prevent flow leakagewhen passive sensing intake 110 is alternatively employed. Like passivesensing, IR source 118 passes infrared waves across IR absorption cell120 to IR filter 124, for measurement by IR detector 126.

The vapor concentrator amplifies the partial pressure of a sample gas,in an embodiment of the present invention. The amplification factor islimited by adsorber's 114 capacity to collect the species of interest.When the limit is exceeded, adsorber 114 begins to saturate, andbreakthrough occurs. Let V_(B) be the volume of sample gas that can bepassed through adsorber 114 before breakthrough. Let V_(S) be the gasvolume in adsorber 114. The maximum possible amplification factor isA=V_(B)/V_(S). Thus, to optimize A, the breakthrough volume should bemaximized relative to the sample volume. One approach is to isolateadsorber 114 as it is heated, for example, by stopping the air flow. Asan estimate, the maximum A is the ratio of the breakthrough volume tothe volume of adsorber 114 itself. The concentration can alternativelybe amplified by rapidly heating adsorber 114 with constant flow of airthrough the vapor concentrator. If this is done, the maximumconcentration depends upon the number of times the air is exchangedwhile heating, so it is important to heat adsorber 114 rapidly.

The safety consequences of drunk driving result from impaired drivingskills and extra risk taking. One approach is to give an impaired drivermore time to react. The present invention provides for automaticcompensation by a safety system for the slowed reaction time of a drunkdriver. For example, if a predetermined concentration of ethanol isexceeded, as measured by the chemical sensor 100 (i.e., an IR sensor),and an ethanol test flag is set to a fail setting, an appropriate safetysystem response can be carried out by an engine microcontroller 140. Thesafety system can impose restrictive requirements and limitationsincluding requiring or increasing a minimum headway distance behind apreceding vehicle, as well as constrain vehicle performance. Further,the safety response can warn and require passengers to fasten seatbelts. Additionally, the safety system can transmit to police, through awireless transmitter, a message that indicates a measured ethanolconcentration or that the ethanol concentration in the vehicle cabin orthe vehicle driver's BAC exceeds a preset level. Further, in anembodiment, in the case of a traffic accident, the safety system canalert an EMS responder or police that ethanol is detected. Additionally,the safety system can transmit any predetermined level of ethanoldetection to a flight recorder for downloading by a third party.

Drunk drivers often take risks while driving. The present invention canbe used to counter this risk taking by warning the driver of the ethanolmeasurement and further require the driver and any passengers toacknowledge the warning. This acknowledgement can issue from a vehiclewarning requiring the use of seat belts. It should be noted that onlyabout 27% of drivers with BAC above 0.08 killed in traffic accidents inthe U.S. were wearing seat belts according to data released by theNational Highway Transportation and Safety Administration. Using a seatbelt (in a vehicle that has airbags) decreases the fatality rate in acrash by about 29%. As an example, in a case where a passive ethanolsensor is installed in all cars and light trucks in the U.S., and alloccupants are wearing seat belts with an intoxicated driver, the use ofseat belts could save about 1,250 lives per year, even with no change indriver risk taking or behavior. However, a change in driver behaviorcould have an even larger impact since, as mentioned above, in 2003 inthe U.S. there were 12,373 deaths in crashes in which a driver had a BACof at least 0.08.

In an embodiment, the safety response further includes monitoring anethanol flag for a failure setting and preventing the vehicle enginefrom restarting for a predetermined number of subsequent vehicle tripsor for a predetermined time period unless, prior to a vehicle trip, theactive breathalyzer measures a driver's BAC as not being legallyintoxicated. The active breathalyzer utilizes the active sensing intake108. In particular, to minimize time inconvenience to a driver in thecase of a safety system preventing vehicle starting, the passivemeasurement mode can be bypassed, and the IR detector 126 used for thepassive measurement mode can be used for a quick breathalyzermeasurement. It is to be appreciated that, in another embodiment, theethanol flag setting can be set or reset to a pass or fail setting asmeasured during a passive measurement, utilizing the passive sensingintake 110. Further, the active breathalyzer measurement mode can clearany ambiguity as to whether an exceeded BAC of ethanol measured by thepassive measurement is due to intoxicated passenger(s), rather than anintoxicated driver.

In an embodiment, the combined passive measurement mode and an activebreathalyzer measurement mode system and method avoids forcing alldrivers to be inconvenienced at every vehicle start. Further, the needto pass an active ethanol measurement is a discouragement to drivingwhile intoxicated. The ethanol flag can serve to alert others, such asparents of a teenage driver, that the vehicle was possibly driven by anintoxicated driver or that ethanol vapor was detected in the vehiclecabin.

The ethanol detection of the present invention can be employed prior tovehicle startup, and can be performed repetitively during vehicleoperation. Repetitive sensing enables the present invention to monitor adriver for previously consumed alcohol that will cause the ethanolconcentration in the driver's breath to increase over time, perhapsabove the legal limit.

Water can condense inside IR absorption cell 120 if IR absorption cell120 reaches a particular low temperature. This can potentially cause anerror in the detection of a small concentration of a particular chemicalvapor from IR transmission since the liquid water on the walls of IRabsorption cell 120 can cause the intensity of transmitted IR todecrease. In an embodiment, the present invention provides the followingadjustments to chemical sensor 100: IR absorption cell 120 is heated toa temperature above the dew point of the vapor released into it fromadsorber 114 or from active sensing intake 108. Alternatively, adsorber114 (carbon) is heated so it is on the order of 10 degrees Celsius aboveambient temperature while the ethanol is being adsorbed. This limits thevolume of water adsorbed by adsorber 114 to avoid exceeding the dewpoint when desorbed vapor is vented into IR absorption cell 120. It maybe that carbon can adsorb water if it is close to the dew point.Alternatively, the inside of IR absorption cell 120 is coated with amaterial that prevents water droplets from nucleating, such as presentlyexisting coatings for vehicle windshields that serve a similar function.Alternatively, the air flow is altered through IR absorption cell 120 sothat exhaust from the vapor concentrator flows down the center of IRabsorption cell 120, but avoids contacting the cool walls where it cancondense. Alternatively, an adsorbent material is utilized that is morehydrophobic than carbon, but still adsorbs ethanol vapor.

FIG. 2 is a logic diagram illustration of the active and passivemeasurement of ethanol vapor by chemical sensor 100. In an embodiment,microcontroller 140 instructs and coordinates the operation of chemicalsensor 100 components including air pump 130, heater 116, IR source 118and IR detector 126. Microcontroller 140 further sets or resets anethanol measurement flag to a pass setting or fail setting, based onmeasured ethanol, utilizing active sensing intake 108 and passivesensing intake 110. Microcontroller 140 also checks for a pass settingand a fail setting of the ethanol flag. It is to be appreciated thatmicrocontroller 140 can alternatively check for the absence of a passsetting or fail setting.

Logic box 210 represents the time when a driver intends to start andoperate a motor vehicle. At this time the driver inserts a key into thevehicle to start the engine. Decision box 212 represents a decisionbased upon whether the ethanol flag is set to a fail setting (or doesnot show a pass setting), in which a counter is checked to determinewhether a predetermined number of trips have elapsed or whether apredetermined time has elapsed since the ethanol flag was previouslyset. This decision can also be made based upon whether both apredetermined number of trips have elapsed and a predetermined time haselapsed. If decision box 212 is determined as being negative, then theflag counter has expired and the engine is permitted to start (logic box232). If decision box 212 is determined as being affirmative, then thedriver is informed that a test is needed to start the vehicle (logic box214). The vehicle driver then utilizes the active sensing intake 108 tomeasure the driver's current BAC (logic box 216). If the driver'smeasured BAC is equal to or greater than the legal BAC limit (decisionbox 218), then the driver is informed that the ethanol test registers afail setting (logic box 220). Additionally, the flag counter is reset toa predetermined number of trips or for a predetermined time duration, orboth (logic box 222). Further, the diver is given the option to repeatthe active test in order to start the vehicle (logic box 214). If thedriver's measured BAC is less than the legal BAC limit (decision box218), then the vehicle engine is permitted to start (logic box 232).

During operation of the motor vehicle, passive ethanol sensing of thevehicle cabin air is performed (logic box 234), employing passivesensing intake 110. This passive sensing is employed to measure adriver's BAC during vehicle operation (decision box 236). If, during thevehicle operation, the passive sensing measures a BAC that is equal toor exceeds the legal limit, the ethanol flag is set to a fail settingand the flag counter is initialized for a predetermined number of tripsor for a predetermined time period, or both (logic box 238). Asdiscussed above, when the ethanol flag is set to a fail setting then asafety system response ensues. In an embodiment, if the passive sensingsets the flag to a fail setting (or not to a pass setting) at any timeduring the vehicle operation, then passengers are warned to fastensafety belts or vehicle performance is constrained or cabin ethanolmeasurements are transmitted to police, or all are performed (logic box240). The subsequent vehicle operator is alerted that an active ethanoltest is needed prior to vehicle usage, since a BAC concentration ofethanol beyond the legal limit was measured during the previous vehicletrip. Alternatively, if, during vehicle operation, the passive sensingmeasures a BAC that is less than the legal limit of intoxication, thepassive sensing measurement is repeated during vehicle operation.

FIG. 3 is a method step illustration of the passive measurement ofethanol vapor with high sensitivity and chemical specificity. Ethanolvapor is collected by passing ambient air into passive sensing intake110 and through adsorber 114 (indicated as method step 310). The IRdetector 126 provides an output voltage (designated V_(off)), with IRsource 118 off (indicated as method step 312). The adsorber 114 isheated by heater 116 to release the captured ethanol vapor (indicated asmethod step 314). The IR source 118 is activated and an output voltage(designated V_(on)) of IR detector 126 is measured without havingconcentrated ethanol vapor in IR absorption cell 120 (indicated asmethod step 316). At a predetermined time, air flow is activated justlong enough to transfer concentrated ethanol vapor from adsorber 114into IR absorption cell 120 (indicated as method step 318). In anotherembodiment, concentrated ethanol vapor is passed from adsorber 114 intoand through IR absorption cell 120 at a predetermined time. Next, thechange in output voltage (designated V_(sig)) of IR detector 126 causedby the additional infrared adsorption, relative to V_(on), is measured(indicated as method step 320). As the concentration of ethanol vapor inIR absorption cell 120 increases, there is a decrease in the IRintensity that is detected. Microcontroller 140 calculates the ratioV_(sig)/(V_(on)−V_(off)) (indicated as method step 322). By activatingthe air flow just long enough to transfer concentrated ethanol vaporfrom adsorber 144 into IR absorption cell 120, the IR transmission canbe measured for a predetermined or long period of time. Air flow isactivated again to purge adsorber 114 and IR absorption cell 120 of anyconcentrated ethanol vapor (indicated as method step 324).

A further understanding of the above description can be obtained byreference to the following experimental result examples that areprovided for illustrative purposes and are not intended to be limiting.

Referring to FIG. 4, a graphical illustration is presented of an examplemeasured voltage as a function of time from IR detector 126 as inFIG. 1. In this example, chemical sensor 100 is sensitive to ethanol andutilizes the passive measurement method steps as described above (whereethanol vapor is passed from adsorber 114 into and through IR absorptioncell 120). As indicated in FIG. 4, “baseline off” extends to about 58seconds, and then a rise in voltage is observed. “Baseline off”corresponds to the time that IR detector 126 provides a measured output(designated V_(off)), with IR source 118 off. At about 58 seconds, IRsource 118 is activated. At about 90 seconds, the output of IR source118 substantially levels off having air in the IR cell absorption cell120, as indicated as “baseline on.” The output from IR detector 126 atthis time is designated V_(on). With IR source 118 on, at apredetermined time, concentrated ethanol vapor is passed from adsorber114 into and through IR absorption cell 120, and a dip in IRtransmission is observed. The dip in output from IR detector 126 isindicated as “desorption peak.” The change in IR detector 126 output(designated V_(sig)) is caused by the additional infrared adsorptionthat occurs, relative to V_(on).

For a sensor that utilizes IR adsorption to determine ethanolconcentration, it is desirable that the output be the ratio of twomeasured quantities. Such a ratio eliminates the gradual drift incalibration that can occur in response to changes such as aging of thelight source or accumulation of material that absorbs infrared on theoptics. The chemical sensor 100 output provided by the present inventionis a ratio. The numerator of the ratio is the integrated “desorptionpeak” versus time (relative to “baseline on”). The denominator is thedifference between “baseline on” and “baseline off.”

It is to be appreciated that a single channel of IR detection isemployed by the present invention, and consequently the chemical sensor100 is less costly to implement. Further, since a reference channel ismade unnecessary, spurious infrared absorption at the IR wavelength ofthe reference channel is not a concern. Additionally, when measuring achemical species, time resolution is not limited by the thermal timeconstant of IR source 118, resulting in a simplified system havingimproved performance.

FIG. 5 is a graphical illustration of an example measured IR sensorsignal ratio versus ethanol concentration obtained utilizing the methodsteps as described above (where ethanol vapor is passed from adsorber114 into and through IR absorption cell 120). As indicated on FIG. 5,ethanol vapor is collected by passing ambient air into and throughadsorber 114 for 5 minutes at 200 sccm (standard cubic centimeter perminute). The flow is stopped while adsorber 114 is heated. Then,concentrated ethanol vapor is passed from adsorber 114 into and throughIR absorption cell 120 at 50 sccm. This process is more fully describedabove with reference to FIG. 3.

Data was collected with known ethanol concentrations in the range of 0to 9 ppm. This ethanol concentration range was selected for experimentsince, as discussed above, an experiment to determine ethanolconcentration produced by a driver with 0.08 BAC found that five minutesafter the driver entered the vehicle, the ethanol concentration in airin the vehicle cabin ranged from about 0.5 ppm to 9.8 ppm. The data wasused to obtain a best-fit linear function of known ethanol concentrationas a function of chemical sensor 100 output. In this example, the datashowed that ethanol concentration was measured with a residual standarderror of 0.13 ppm. The chemical sensor 100 (as in FIG. 1), with regardto passive measurement, satisfactorily measures ethanol concentration inthe range of 0.1 ppm to 10 ppm, and therefore provides sufficientsensitivity for passive detection of an intoxicated vehicle driver withBAC near the threshold of legal intoxication. Additionally, sincedrivers can exhibit a BAC of much greater than 0.08, and the vehiclecabin air may be less diluted, the present invention further providesfor measuring ethanol concentrations greater than 10 ppm.

Referring to FIG. 6, a graphical illustration is presented of an examplemeasured voltage as a function of time from the IR detector 126 as inFIG. 1. The chemical sensor 100 is sensitive to ethanol, utilizing themethod steps as in FIG. 3 (where air flow is activated just long enoughto transfer concentrated ethanol vapor from adsorber 114 into IRabsorption cell 120). In this particular example, the ethanolconcentration in the air is 4.3 ppm.

Carbon dioxide is also measured by pulsing IR source 118 on and off asair is passed through adsorber 114 and IR absorption cell 120. Carbondioxide is not adsorbed by adsorber 114. The resulting effect of thispulsing can be observed from about time=0 to time=120, as the voltagejumps to about −0.068 V. Next (as more fully described in FIG. 3), IRsource 118 is turned off for about 5 seconds to obtain a “baseline off”value. Subsequently, IR source 118 is activated and adsorber 114 isheated for a predetermined time. The IR detector 126 output voltage iselevated to the “baseline on” value. About 3 seconds later, air pump 130is activated for 0.2 seconds, transferring concentrated ethanol vaporinto IR absorption cell 120, causing the IR transmission to decrease toa constant value. This constant decreased IR detector 126 output voltagecan be maintained as long as the concentrated ethanol vapor remains inIR absorption cell 120, as desired. Next, air pump 130 is activatedpurging adsorber 114 and IR absorption cell 120 of concentrated ethanolvapor. The IR detector 126 output voltage returns to its elevated“baseline on” value. Subsequently, at about 195 seconds, the IR source118 is turned off and the IR detector 126 output voltage drops. Again,it is to be appreciated that the time periods described in FIG. 6, aswell as other time periods described herein, are provided forillustrative purposes and are not intended to be limiting. Other timeperiods can be employed.

A person with ethanol in their blood tends to evaporate ethanol vaporfrom their skin into fresh air. Ethanol leaves the body through the skinin two ways. Ethanol in the blood can diffuse through the skin todirectly enter the air as ethanol vapor. Additionally, under somecircumstances, liquid sweat is formed. Liquid sweat contains ethanol atthe same concentration as blood. Ethanol in sweat evaporates to formethanol vapor in the air. However, the fraction of ingested alcohol thatescapes through the skin is only about 1%, so it does not have asignificant effect on the average concentration of ethanol vapor in avehicle cabin. For these reasons, and more, the placement of passivesensing intake 110 is important to more reliable ethanol concentrationmeasurements.

As illustrated in FIG. 7, the present invention provides alternativeplacement/mounting options of the passive sensing intake 110 in avehicle cabin for the chemical sensor 100 as in FIG. 1.

It is important to note that exhaled breath from a vehicle driver ismixed with and diluted with air as it drifts to the ethanol samplinglocation (passive sensing intake 110). The dilution factor depends uponvariables such as the speed of the fan blowing fresh air into the cabin,vehicle speed, the settings and directions of the air vents, and thelocation of the driver's mouth relative to the ethanol sensor. In asimple approximation, breath and air are fully mixed in the cabin beforethey arrive at the ethanol sensor. An adult male driver typicallyexhales 10.8 liters per minute; an adult female driver 9.0 L/min. Themaximum air flow from the HVAC (heat-ventilation and air-conditioning)system into a vehicle is typically 7080 to 8050 liters per minute (250to 300 cubic feet per minute). This suggests that in steady state, thedilution factor could be as low as 1.3×10⁻³, and that a passive ethanolsensor should be capable of measuring ethanol vapor concentrations aslow as 0.3 ppm. Further, the volumetric breathing rate varies fromperson to person and is related to physical exertion. The volumetricbreathing rate of a subject person must be accounted for to determinethe minimum ethanol concentration that is needed for detection.

The vehicle driver's BAC is measured by sensing the concentrations ofethanol vapor in air sampled near the driver. The present invention canmeasure ethanol vapor concentration at one or more location in thevehicle cabin by placement of passive sensing intake 110 in one or morevehicle cabin locations. Further, the chemical sensor 100 can besituated in an inconspicuous location and operate independently withoutrequiring active involvement by a driver.

For maximized passive ethanol sensitivity to the vehicle driver, it ispreferable for the sensor to be exposed to the driver's breath beforethe driver's breath completely mixes with cabin air. Additionally, sincea driver and a number of passengers may be present in the vehicle cabin,in an embodiment of the present invention, passive sensing intake 110 issituated directly adjacent to a vehicle driver. For example, as shown inFIG. 7A, passive sensing intake 110 is incorporated into the vehiclesteering wheel or steering column. Additional passive sensing intake 110placement locations are shown in FIG. 7B and FIG. 7C. Passive sensingintake 110 as shown in FIG. 7B can be incorporated into the vehicleceiling or dashboard (preferably distant from an air exhaust vent).Alternatively, passive sensing intake 110 can be incorporated into avehicle body intake vent as shown in FIG. 7C. Further, passive sensingintake 110 can be incorporated into the vehicle headrest, seat, A pillaror B pillar.

FIG. 8 is a diagrammatic view showing alternative placement options ofthe active sensing intake 108, for the chemical sensor 100 as in FIG. 1.The present invention can measure ethanol vapor concentration by anactive measurement mode taken in a variety of locations in or outsidethe vehicle cabin. Further, active sensing intake 108 can be situated inan inconspicuous location where, for example, active sensing intake 108extends and retracts from a position having a concealing cap or cover.Active sensing intake 108 can be situated directly adjacent to a vehicledriver. For example, as shown in FIG. 8A, active sensing intake 108 isincorporated into the vehicle steering wheel or steering column.Additional active sensing intake 108 placement locations are shown inFIG. 8B, mounted on top of, or incorporated into, the dashboard.

Other features and advantages of this invention will be apparent to aperson of skill in the art who studies this disclosure. For example, itis to be appreciated that on-board passive ethanol vapor sensors coulduse a vapor concentrator in conjunction with alternative detectiondevices including a floating-gate field effect transistor, a gaschromatograph, a heated metal-oxide film sensor, a sensor that measuresoxidation luminescence, a CMOS capacitive sensor that uses a polymerfilm, and a photoacoustic sensor. Further, higher sensitivity is alsopossible with more elaborate spectroscopic techniques. If a narrow-linelaser source is used, its optical frequency can be tuned to one side ofa narrow feature in the spectrum, and the laser frequency can be sweptback and forth to modulate the transmitted intensity. Sensitivityimproves by orders of magnitude if the gas to be analyzed is at apressure on the order of 1 Pa. Thus, exemplary embodiments,modifications and variations may be made to the disclosed embodimentswhile remaining within the spirit and scope of the invention as definedby the appended claims.

We claim:
 1. A method of measuring a chemical vapor concentrationcomprising: providing a chemical vapor passive sensor; passing air,including sample vapor, through an adsorber; measuring a first output(designated V_(off)) of an infrared detector, with an infrared sourcedeactivated; heating the adsorber; measuring a second output (designatedV_(on)) of the infrared detector, with the infrared source activated;passing concentrated sample vapor from the adsorber into and through aninfrared absorption cell; measuring a change in an third output(designated V_(sig)) of the infrared detector; and calculating a ratioV_(sig)/(V_(on)−V_(off)).
 2. The method of measuring a chemical vaporconcentration as in claim 1, wherein passing concentrated sample vaporfrom the adsorber into and through the infrared absorption cellcomprises: activating air flow just long enough to transfer concentratedsample vapor from the adsorber into the infrared absorption cell;holding the concentrated sample vapor in the infrared absorption cellfor a predetermined and desired time; and activating air flow again topurge the adsorber and the infrared absorption cell of the concentratedsample vapor.
 3. The method of measuring a chemical vapor concentrationas in claim 1, wherein passing air, including the sample vapor, throughthe adsorber comprises passing vehicle cabin air through the adsorber,and wherein the sample vapor is ethanol vapor.
 4. The method ofmeasuring a chemical vapor concentration as in claim 1, wherein amicrocontroller calculates the ratio V_(sig)/(V_(on)−V_(off)), andinstructs and carries out a safety response.
 5. The method of measuringa chemical vapor concentration as in claim 1, wherein the method furtherincludes the steps of: providing a chemical vapor active sensor; passingunmixed gas into the infrared absorption cell; and measuring an unmixedgas infrared absorption within the infrared absorption cell with theinfrared source activated, utilizing the infrared detector.
 6. Themethod of measuring a chemical vapor concentration as in claim 5,wherein passing unmixed gas comprises passing human breath, whereinmeasuring the unmixed gas infrared absorption comprises measuringethanol infrared absorption, and wherein a first predeterminedconcentration is less than 210 parts per million (ppm).
 7. The method ofmeasuring a chemical vapor concentration as in claim 6, furthercomprising imposing a safety response when the chemical vapor activesensor detects that the sample vapor exceeds the first predeterminedconcentration, wherein the safety response includes at least one ofsetting a flag counter which requires an active breathalyzer test(utilizing the chemical vapor active sensor) for at least one of apredetermined number of vehicle trips and a predetermined time toprevent a vehicle engine from restarting until a driver's BAC ismeasured as a level established as legal to operate a motor vehicle. 8.The method of measuring a chemical vapor concentration as in claim 5,further including the steps of: utilizing the chemical vapor passivesensor when one of: a flag is set to a pass setting, and a chemicalvapor active sensor detects that a first chemical vapor concentration isbelow a first predetermined concentration; utilizing the chemical vaporactive sensor when the flag is set to a second setting; setting the flagto the first setting when the chemical vapor passive sensor is utilizedand detects that a second chemical vapor concentration is within asecond predetermined concentration range; and setting the flag to thesecond setting when the chemical vapor passive sensor is utilized anddetects that the second chemical vapor concentration exceeds the secondpredetermined concentration range.
 9. The method of measuring a chemicalvapor concentration as in claim 8, further comprising imposing a safetyresponse when the chemical vapor passive sensor detects that the samplevapor indicates that a vehicle occupant exceeds a legal blood alcoholconcentration (BAC) for a driver, wherein the safety response includesat least one of setting the flag to the second setting, setting a flagcounter which requires an active breathalyzer test, utilizing thechemical vapor active sensor, for at least one of a predetermined numberof vehicle trips and a predetermined time to prevent a vehicle enginefrom restarting until a driver's BAC is measured as a level establishedas legal to operate a motor vehicle, warning passengers to fasten seatbelts, increasing a minimum headway distance behind a preceding vehicle,constraining vehicle performance, transmitting vehicle cabin ethanolmeasurements to police and to a vehicle recorder.
 10. The method ofmeasuring a chemical vapor concentration as in claim 8, furthercomprising at least one of utilizing the chemical vapor active sensorwhen the flag is set to first, and utilizing the chemical vapor passivesensor when the flag is set to second.
 11. The method of measuring achemical vapor concentration as in claim 10, wherein the first settingis the pass setting and the second setting is a fail setting.